Let's have more leap seconds

From: Ed Davies <ls_at_edavies.nildram.co.uk>
Date: Mon, 11 Aug 2003 12:07:35 +0100

Thinking about Steve Allen's post about a problem with the
Motorola Oncore GPS receivers caused by the recent lack of
leap seconds I began to wonder if we ought not to have a
lot more leap seconds.

Suppose that instead of leap seconds only being inserted
when required to minimize |UT1-UTC| they were inserted
whenever possible. That is, whenever they can be inserted
without risking |UT1-UTC| > 0.9s.

This would mean that nearly 80% of months would have leap
seconds. Generally there'd be an alternating sequence of
positive and negative leap seconds.

This would not eliminate the possibility of a problem like
that of the Oncore because there could be a long period
with close to 86 400 second days where UT1-UTC happens also
to be too close to zero (magnitude less than just over 0.1)
to allow a leap second to be inserted.

It would also increase the average magnitude of UT1-UTC
(from something just over 0.25 to about 0.45) but who
actually cares what the average is? You have to plan for
the worst case according to the specification (0.9s) anyway
- anybody who assumes it'll never go much over 0.5 deserves
whatever happens.

The advantage of this scheme would be that systems would
usually be tested for correct operation over leap seconds
early in their life, ideally during testing or commissioning,
and anyway when things are still fresh in people's minds.

It would be a bit of a nuisance for systems which require
manual intervention for leap seconds but at least the
operators would get some practice. An example would be the
UKIRT in Hawaii which, if I understand the manual properly,
can't interpolate Earth orientation over a leap second. A
minor problem for an optical telescope in Hawaii but a major
one for one on Tenerife.

(Actually, I think USAF IR telescopes on Hawaii do operate
during the day and therefore potentially over a leap second -
the Shuttle Columbia was imaged at, IIRC, about 11 in the
morning local time.)

It would also ensure that systems work properly when there
are multiple leap seconds scheduled and for a variety
of signs and magnitudes of UT1-UTC.

I know this sounds like a silly idea but I do think it has
some merit. Either you can handle leap seconds, in which
case extra ones are little trouble, or you can't in which
case you need to find out as soon as possible. Essentially,
it reduces one of the problems with leap seconds: that they
are rare events.

Ed Davies.
Received on Mon Aug 11 2003 - 04:13:18 PDT